An engine may include valve operators to selectively activate and deactivate engine intake and exhaust valves. By deactivating selected engine intake and exhaust valves in a closed position and ceasing to inject fuel, cylinders may be deactivated and the displacement of an engine may be effectively reduced. At lower engine loads, it may be desirable to deactivate engine cylinders to reduce engine displacement to reduce engine pumping work and increase the efficiency of active (e.g., cylinders combusting air and fuel) cylinders. At higher engine loads, all engine cylinders may be activated to increase engine output. The engine may switch between deactivating cylinders and all active cylinders. Conventional thinking may lead one to believe that as long as engine torque requirements may be met when engine cylinders are deactivated, deactivating cylinders conserves fuel. However, deactivating engine cylinders may not always increase engine efficiency for at least the reason that cylinders that remain active may be moved to a borderline spark limited knock region where engine fuel economy decreases. Therefore, it may be desirable to provide a way of determining whether or not deactivating engine cylinders conserves fuel.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating an engine, comprising: estimating a plurality of engine fuel consumption values for operating an engine with a plurality of configurations including different actual total numbers of active cylinders; and operating the engine including an actual total number of active cylinders based on the plurality of engine fuel consumption values.
By determining a plurality of fuel consumption values for an engine with a plurality of different available actual total numbers of active cylinders, it may be judges which cylinder modes provide an increase in fuel economy so that the engine may be operated in a mode that conserves fuel. For example, if a four cylinder engine provides 100 N-m of torque at 3000 RPM and consumes X liters of fuel per hour in four cylinder mode, and the same engine provides 100 N-m of torque at 3000 RPM and consumes X−0.2 liters of fuel per hour in two cylinder mode, the engine is operated in two cylinder mode. On the other hand, if a four cylinder engine provides 150 N-m of torque at 4000 RPM and consumes Y liters of fuel per hour in four cylinder mode, and the same engine provides 150 N-m of torque at 4000 RPM and consumes Y+0.2 liters of fuel per hour in two cylinder mode, the engine is operated in four cylinder mode.
The present description may provide several advantages. For example, the approach may improve vehicle fuel economy. In addition, the approach may provide a basis for selecting a more useful cylinder mode from a plurality of cylinder modes. Further, the approach may augmented with vibration sensor information to ensure engine vibration does not exceed a threshold in the selected engine operating mode.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.